A. Field of the Invention
The device of the present invention generally relates to gas tube voltage breakdown devices, often commonly referred to as surge arresters, and, more particularly, to a new and improved hermetically sealed gas tube voltage breakdown device having a ceramic insulating spacer and a trigger electrode and particularly adapted for repetitive use as a voltage breakdown device in an electrical circuit, for example, in an electrical circuit for controlling the light output of a photoflash lamp.
B. Description of the Prior Art
Hermetically sealed gas tube voltage breakdown devices, commonly known as and used as surge arresters, are old and well-known in the art. For example, pertinent prior art gas tube voltage breakdown devices or surge arresters are disclosed in U.S. Pat. Nos. 3,588,576; 4,084,208; and 4,287,548. Typically, such devices are used as surge arresters to protect electrical equipment from damage or destruction due to the presence of overvoltage surges. However, such devices also have been used in electrical circuits requiring a voltage breakdown device capable of conducting relatively high currents.
In the prior art, electrical circuits have been used to control the light output of photoflash lamps. Such circuits generally supply high voltage across a capacitor to store a charge for lighting a photoflash lamp. In addition, switching means in the form of a manual switch or a photoresistor are used to extinguish the photoflash lamp when sufficient illumination has been provided. Examples of circuit elements used to extinguish the photoflash lamp by electrically shorting a storage capacitor and/or the photoflash lamp are cold cathode thyratrons or hermetically sealed gas tube voltage breakdown devices or surge arresters utilizing glass spacer tubes. Glass spacer tubes used in such an application have included a trigger electrode disposed about the glass spacer tube in the region of the electrode gap to increase the electric field intensity in that region upon the presence of a trigger pulse, thereby to cause the sparkover or breakdown of the electrode gap and electrical current conduction through the voltage breakdown device.
Generally, the life expectancy of a voltage breakdown device with a glass spacer tube used in such an application is relatively short since the glass spacer tube tends to become embrittled. The use of a gas tube voltage breakdown device utilizing a ceramic spacer tube would result in a higher life expectancy since the ceramic would not become embrittled and deteriorate as rapidly as the glass spacer tube. However, due to the significantly higher dielectric constant of the ceramic spacer tube as compared to the glass spacer tube, the application of an external trigger pulse in the region of the electrode gap of a typical ceramic gas tube voltage breakdown device would have an insufficient effect upon the electric field intensity in that region and would thus be unsuitable for causing sparkover or gap breakdown and current conduction through the voltage breakdown device.